Cytochrome c oxidase is the mitochondrial enzyme which mediates the oxidation of ferrocytochrome c (cyt c) by molecular oxygen. It is also one of three points in the electron transport chain at which ATP is synthesized. A detailed mechanism for these processes is not yet in hand. There is recent evidence for profound allosteric interactions in cytochrome oxidase, yet not much study has been devoted to the effects of cyt c on them. We propose to investigate this question here. First, active-enzyme band sedimentation studies, in which a band of oxidase is sedimented through a column of ferrocyt c, should detect conformational changes due to interaction between them. Second, oxidase complexes with various ligands are to be titrated with ferrocyt c, and monitored at characteristic absorption bands. The results should characterize patterns of interaction between the redox sites in the oxidase, which will differ for the different ligands. Third, binding studies between cyt c and different oxidase complexes should detect conformational effects, due to ligation and redox level changes, which are transmitted to the binding site for cyt c. The results should deepen our understanding of the pathways of electron transfer in cytochrome oxidase as molecular oxygen is reduced. The structural and functional interactions to be elucidated are likely to increase our comprehension of control mechanisms in electron transfer and the mediation of ATP synthesis in the mitochondrion. This new knowledge would be of universal importance in further understanding of cellular metabolism. BIBLIOGRAPHIC REFERENCE: "Reversible Inactivation of Cytochrome c Oxidase by SH-Specific Hydrophobic Reagents", A. J. Mann and H. E. Auer, Abstract, 175th Meeting, American Chemical Society, August, 1977, in press.